Periodic wave generator



Nov. 12, 1946. J. c. WILSON PERIODIC WAVE GEi fiRA ToR Filed Aug. 26,1938 FIG.2.

FIG. I.

FIG.4.

FIGS- INVENTOR JHN C.WILSON BY 0 l k l 1 I ATTORNEY Patented Nov. 12,1940 John C. Wilson, Bayside, N. Y, assignor to Hazeltine Corporation, acorporation of Delaware Application August 26, 1938, Serial No. 226,874

' 8 Claims.

ators and, while the invention is of general ap plication, the generatorof the invention is particularly suitable for deriving from a given wavea wave of submultiple frequency for use as a timing wave in a televisionsignal transmitter.

In generating timing pulses in a modulatedcarrier television signaltransmitter, some of which form components of the transmitted s ig nals,it is customary to generate high-frequency waves which are stabilizedwith respect to the source of alternating current at the transmitter andto derive therefrom waves of submultiple frequencies. -Thesubmultiple-frequency waves so developed are used for the various timingoper-,

ations necessary to generate and transmit .the

For example, in decomposite television signal. veloping and transmittinga television signal involving double interlaced scanning and 441 linesper second, it is customary to develop a high-frequency. wave, forexample, 26,460 cycles, which is stabilized with respect to a source of60 cycle power supplying the transmitter. From this high-frequency wavethere is derived-a submultiple-frequency wave of 13,230 cycles, that is,half the frequency of the high-frequency wave, which is utilized toproduce line-frequency synchronizing pulses for the transmitted signal.By a further series of subdivisions, a 60 cycle wave is developed andutilized to provide field-frequency pulses for the transmitted signal. Ahigh degree of accuracy is essential in the relation between thefrecuenciesof the difierent wave generators which go to make up thetimer chain of the sys- 35 tem. For this reason it is customarytodevelop the waves in the manner described above rather than to generatewaves of increasingly higher frequencies from the low-frequency sourcesup- Ply the transmitter. However, in subdividing a generated high-frequency wave to derive the waves oiflower' 1re-,

quency, it is difficult to secure generators or frequency dividers foreach oi the steps which are not subject to some inaccuracies. If aparticular wave generator of lower frequency is to produce pulses of afrequency of 1/11. times that of a higher frequency control wave, it iscustomary to provide a control circuit for the generator which isresponsive to pulses in the control wave which are separated by n-lpulses. The usual way of accomplishing this is to provide a relaxatibnoscillator including a vacuum tube having a control electrode to whichthe desired pulses at are supplied. One particular circuit which haswave.

This invention relates to periodic wave gener- 7 been utilized comprisesa condenser which is alternately charged from a direct current sourceand discharged, one of the operations being controlled by a' vacuumtube. In this type of circuit the activeperiod of the tube depends notonly on 5 the control wave, usually applied to the control grid, butalso upon the voltage of the condenser which is effectively coupled intothe anode circuit of the tube'and thereby affects its anode voltage. Inprevious circuits of this type, the 1g condenser is charged relativelyslowly, either linearly or exponentially, and discharged rapidly, orvice versa. As a result, the anode voltage rises to a substantial valueduring the initial portion of the linear or exponential charge ordischarge is and the slope of the anode voltage wave durin 7 the.finalportion of this period is of relatively low value so that the controltube'm'ay be controlled by a wrong pulse in the controlling wave, or bysome extraneous influence, such as static. an

', That is, the system is much too sensitive to controlling effects onits control electrode over substantially all of the linear orexponential charging or discharging periods.

It is an object of the invention to provide a 28 periodic wave generatorwhich is not subject to the above-mentioned disadvantages.

It is a further object of the invention to provide a periodic wavegenerator which is've-ry insensitive to a control wave, except duringportions of each cycle when the control wave shouldbe effective. 7

It is a further object of the invention to provide a periodic wavegenerator which is very insensitive with respect to any externalinfluence, .35 except during a small portion of each cycle within whichit is desired externally to influence the generator. V p

In accordance with the invention, a periodic wave generator adapted tobe excited or fired by 40 selected pulses of a periodic-pulse wave whichmay include disturbing spurious pulses, comprises a capacitance meanshavingcharging and discharging circuits, the voltage across the.capacitance meanscomprising-the desired voltage 45 Means are provideddependent at least in part upon the voltage of the capacitance means forcontrolling the charging and discharging circuits periodically andalternately to charge and' discharge the capacitance means. Thegenerator I0 also includes means for decreasing materially thesusceptibility to firing by undesired pulses occurring between theselected pulses comprising impedance means included in one of thecharging or discharging circuits, the impedance of the imparticularityin the appended claims.

pedance means being so proportioned with respect to the impedanceconstants of said one circuit that the slope of the voltage-timecharacteristic of the capacitance means during the greater portion ofthe final half of the active period .of said one circuit issubstantially greater than that of a linear voltage-time characteristicbetween the same charging voltage limits of the capacitance means. i

In a preferred embodiment of the invention, a direct current circuit isprovided for charging a condenser having the above-mentioned imped timemeans in circuit therewith and the control tube is utilized to dischargethe condenser. The control tube is provided with. a control electrode towhich may be appliedcontrol pulses. In this preferred embodiment,therefore, the impedance -means prevents the voltage across thecondenser fromrising to the critical value, that is, above the value itmust have before the tube can be controlled by the pulses on the controlgrid, until such time as it is desired to control the tube. The circuitis thus very insensitive over nearly all of its charging cycle.

The novel features which are believed to be characteristic of thisinvention are set forth with vention itself, however, both as to itsorganization and method of operation, together with further objects andadvantages thereof, will best be understood by reference tothe followingdescription taken inconnection with the accompanying drawing, and itsscope will be pointed out in the appended claims.

Fig. 1 is a simplified circuit diagram of a periodicwave generatorembodying the invention; Fig. 2 illustrates the voltage timecharacteristics of a circuit similar to that of Fig. 1, if the chargingcircuit of the. invention is not utilized; Fig. 3 illustrates thecharacteristics of the circuit of Fig. 1 having constants proportionedin accordance with the invention; Fig. 4 is a circuit diagram of afurther embodiment of the invention; Fig. 5 illustrates certainoperating characteristics of the circuit of Fig. 4; and Fig. 6 is acircuit diagram of a periodic-wave generator similar to that of Fig. 1but comprising a high vacuum tube provided with regenerating means.

Referring now more particularly to the drawing, in Fig. 1 there is showna periodic wave generator comprising a capacitance means l0 which ischarged from a battery ll through a circuit comprising a resistor l2 andan inductance l3. Thedischarging circuit comprises a vacuum tube H,preferably of the vapor electric discharge type, having outputelectrodes connected across condenser and having its control gridnormally biased to cutofi by means of a source of voltage,

' indicated as -C, applied through a resistor l5.

Neglecting for the present the featuresof the circuit of Fig. 1constituting the present invention, the wave generator described issimilar to those whichhave previously been used and its operation iswell understood in the art. Briefly, however, condenser l0 is'.chargedexponentially from battery H during the period t1, tz (see Fig. 2) andis-discharged by vacuum tube I4 during the time ta, ta, this cycle beingindefinitely repeated. The periodic voltage across the condenser 10 maybe utilized directly as, or may be utilized to derive, a secondary waveof a desired frequency. The wave A of Fig. 2 indicates a source ofhigh-frequency pulses which may be applied to the control electrode ofelectron dis- The incharge device It, each of the pulses .beingsuflicient to bias the tube above its cutoff value dur-' the dischargecircuit of the capacitance means I0 is jointly controlled in accordancewith the voltage of the capacitance means and predetermined pulses ofthe wave A applied to its control electrode, and the tube, therefore,comprises means dependent at least in .part upon the voltage of thecapacitance means for controlling the charging and discharging circuitsperiodically and alternately to charge and discharge the capacitancemeans. Curve B of Fig. 2 indicates the voltagetime characteristic duringthe charging period of condenser l0 and it is seen that, at the time t4,the condenser voltage and, therefore, the anode voltage of tube l lrises above the critical value Vc and the tube may, therefore, be madeconductive by pulse C, whereas it is desired that the generator shouldbe insensitive to pulse C and should be controlled by pulse D.Furthermore, due to the relatively large voltage applied to the anode oftube l4 during times in the vicinity of pulseC, extraneous influences,such as static pulses, may easily cause tube It to become conductiveeven though pulse C itself did not have this effect.

In accordance with the present invention, inductance element I3 isinserted in ,the charging that of the resistor [2 are so proportionedrelative to the impedance constants of the charging circuit comprised inlarge part by condenser l0 as to modify the time-voltage characteristicfrom that of curve B of Fig. 2 to that of curve B, shown in Fig. 3. Thehigh-frequency wave A of Fig. 3 is identical with that of Fig. 2. It isseen that the amplitude of the voltage time characteristic B ofcondenser ill at any predetermined time during its active or chargingperiod is substantially less than that of characteristic B at acorresponding instant of time over substantially all of the activeperiod. Consequently, the amplitude of the voltage appearing across thecapacitance means I0 at any predetermined time during the greaterportion of the final half of the active period of the charging circuitis substantially less than that resulting from a linear voltage-timecharacteristic between the same charging voltage limits of thecapacitance means. Therefore, during such period, the voltage of thecondenser 10 does not rise dangerously close to the critical voltage V0and the generator is not likely to be affected by'extraneous pulses-ortram-- greater than that of a linear voltage-time characteristic a, ,bbetween the same charging voltage limits V2V1 of condenser 10. It isthus evident that the amplitude of the voltage appearing across thecondenser ID at any predetermined time during the greater portion of thefinal half of the charging period .t1t2 is substantially less than thatof a linear voltage-time characteristic between the same chargingvoltage limits V1v2 1'8 of the condenser. Therefore, the tube It is notresponsive to the premature pulse C but only to the desired pulse D andis less likely to be trippedv by extraneous transients occurring in timein the vicinity of pulse C. Thus, the system includes Tube 14 Type 884Capacitance 10 micro farad.. 0.05. Battery 1 1; volts 170 Resistance 12'ohms 5,000 Inductance 13 henrie s 20 Normal operating freguency cycles'60 The circuit of Fig.4 difiers from that of Fig. 1 primarily in. thefact that a vacuum tube 20 has been provided for effectively opening orinterrupting the charging circuit of condenser I during the intervalwhen condenser I0 is beingdischarged through tube 14. Similar circuitelements have been given similar reference numer- I erably-are asfollows:,

als in the two figures.

charging circuit comprising series-connected in ductance l3 and resistor12, while a resistor 2| is included in the discharge circuit ofcondenser l0 and in the input circuit of tube 20.

In considering the operation of the circuit of Fig. 4, it will be seenthat, when tube I4 becomes conductive to discharge condenser 10, anappre-- ciable voltage is developed across resistor 2| by the dischargecurrent which voltage is applied to the control electrode of vacuum tube20, thereby to bias the same-beyond its cutoff value and effeotivelyopen the charging circuit of the system.

The characteristics of the wave generator of Fig. 4 .are illustrated inFig. 5 from which. itis seen that, byopening the charging circuit of thecondenser III while the condenser is being discharged, the amplitude ofthe condenser voltage is further decreased during the initial portion of.the charging period and the slope of the charging voltage time curve ofcondenser I0 is further increased during the final portion of thecharging period. This is shown by curve B of Fig. 5. From this curve, itis seen that the amplitude of the voltage across the condenser III atany predetermined time during the final half ts-tr of the chargingperiod t1-tz is even less than that resulting from the voltage-timecharacteristic of the Fig. 1 arrangement, as indicated by the curve ofFig. 3,

and. especially is this so during the relatively shortinterval ts-tzwhich immediately precedes the desired synchronizing pulse D. Therefore,the

circuit of Fig. 4 is much less sensitive overthe initial portion of .thecharging periodthan the circuit of Fig. 1 and is at least equallysensitive to the desired synchronizing pulses near the end of thecharging period. Thus, resistor 2| comprises impedance means -in,circuitwith vacuum tube 20 for controlling the periods of conductivity of thistube.

One set of values for the circuit of .Fig. 4 pref- Tube 14 Tube 20 Type605 Resistance21 Between 100 and 500 ohms- The output electrodes ofvacuum tube 20 are connected directly in the ype,884 f The other valuesremain the same as those giv en above for Fig. 1. I

While there-has been described a periodic wave generator comprising avapor electric discharge tube for discharging the condenser, it will beunderstood that the principles of the-invention are equally applicableto'an arrangement, as shown by Fig. 6, utilizing a high vacuum tube '18ineluding suitable regenerating-means, comprising inductively coupledwindings 11, I8, to change the conductivity of the tube from minimum tomaxias that of Fig. 1 of Patent 2,148,096, issued February 12, 1939, toG. B. Banks. Further, the vacuum tube may be included in the chargingcircuit of thecondenser rather than the discharging circuit,- as shownby Patent 2,118,352, dated May 24, 1938, in which case the dischargecircuit-isproportioned in accordancewith the above prin-' ciples.

mum for a small difference in grid voltage such While there has beendescribed what is at present considered to be the preferred embodimentof this invention, it will be obvious to those skilled in the art thatvarious changes and modifications may be made therein without departingfrom the invention, and it is, therefore, aimed in the appended claimsto cover all such changes and modifications as fall within the-truespirit-andscopeof the invention. a What is claimed is: V 1. A periodicwave generator adapted to be fired by selected pulses of aperiodic-pulse wave which may include disturbingspurious pulses,

comprising capacitance means, charging and discharging circuits for saidcapacitance means, means dependent at least inpart upon the voltage ofsaid capacitance means for controlling said circuits periodically andalternately to charge and discharge said capacitance means, and meansfor decreasing materially the susceptibility to firing by undesiredpulses occurring, between said selected pulses comprising impedancemeans 1m;

cludedin one of said circuits, the impedance of said'impedance meansbeing so proportioned with respect to the impedanceconstants of said oneof said circuits that the slope of the voltage-time characteristic ofsaid capacitance meansduring .the greater portion of the final half ofthe active period of said one of said circuits is substantially greaterthan thatof a linear voltage-time characteristic between the samecharging voltage limits of said capacitance means.

2. A periodic wave generator adapted to be fired I 4 by selected pulsesof a periodic-pulse wave which may include; disturbing spurious pulses,comprising capacitance means, charging and dis-- charging circuits forsaid capacitance means, means dependent at least in part upon thevoltage of said capacitance means for controlling said circuitsperiodically and alternately to charge and discharge said capacitancemeans, and means for decreasing materially the susceptibility to firing.

by undesired pulsesoccurring'between said se-v lected pulses comprisingimpedance means included in one of 'said circuits, said impedancemeans-being so proportioned with respect to the reactive constants ofsaid one of 'said circuits that the amplitude of the voltage. appearingacross said capacitance means at.any predetermined time during thegreaterportion of the final half of the active period of said one ofsaid circuits is s'ubstantially less than that resulting from a linearvoltage-time characteristic between the same.

charging voltage limits of said capacitance means.

.. 3. A periodic wave generator adapted to be fired lected pulsescomprising means including a seriesconnected inductance and resistor inone of said circuits, the values of said inductance and said resistorbeing so proportioned with respect to the value of said capacitancemeans that the amplitude of the voltage appearing across saidcapacitancemeans at any predetermined time during the greater portion ofthe final half of the active period of said one of said circuits issubstantially less than that resulting from a linear voltage-timecharacteristic between the same. charging voltage limits of saidcapacitance means.

4. A periodic wave generator adapted to be fired by selected pulses of aperiodic-pulse wave which may include disturbing spurious pulses,comprising capacitance means, charging and discharging circuits for saidcapacitance means, means comprising a vacuum tube included in one ofsaid circuits controlled at least inpart in accordance with the voltageof said capacitance means for controlling said circuits periodically andalternately to charge and discharge said capacitance means, and meansfor decreasing materially the susceptibility to firing by undesiredpulses occurring between said selected pulses comprising impedance meansincluded in the other of said circuits, said impedancemeans being sopro-,

portioned with respect to said capacitance means that the amplitude ofthe voltage appearing across said capacitance means at any predeterminedtime during the greater portion of the final half of the active periodof said one of said 'circuits is substantially less than that resultingfrom a linear voltage-time characteristic between the same chargingvoltage limits of said capacitance means.

' 5. A periodic. wave generator adapted to be fired by selected pulsesof a periodic-pulse wave which may include disturbing spurious pulses,comprising capacitance means, charging and discharging circuits for saidcapacitance means,

, means dependent atleast in part upon the voltage of said capacitancemeans for controlling said circuits periodically and alternately tocharge and discharge saidcapacitance means, and means for decreasingmaterially the susceptibility to firing by undesired pulses occurringbetween said se lected pulses comprising impedance means included in oneofsaid circuits, said impedance means being so proportioned with respectto said capacitance means that the amplitude of th voltage appearing,across said capacitance means at any predetermined time during thegreater portion oi: the-final half of the active period of said one ofsaid circuits is substantially less than that resulting from a linearvoltage-time characteristie between the same charging voltage limits offired by selected pulses of a periodic-pulse wave which may includedisturbing spurious pulses,

comprising capacitance means, a charging circuit for said capacitancemeans, means comprising a vacuum tube controlled in accordance with thevoltage across said capacitance means for discharging said capacitancemeans at periodic intervals, andmeans for decreasing materially thesusceptibility to firing by undesired pulses occurring between saidselected pulses comprising impedance means included in said chargingcircuit, said impedance means being so proportioned with respect to theimpedance constants of said charging circuit that the amplitude of thevoltage appearing across said capacitance means at any predeterminedtime during the greater portion of the final half of the charging periodof said capacitance means is substantially less than that resulting froma linear voltage-time characteristic between the same charging voltagelimits of said capacitance means, and means including a vacuum tubeincluded in said charging circuit for effectively interrupting saidcharging circuit during the discharge period of said capacitance meansto decrease further the amplitude of the voltage appearing across saidca-.

pacitance means during the said greater portion of the final half ofsaid active period.

'7. A periodic wave generator adapted to be fired by selected pulses ofa periodic-pulse wave which may include disturbing spurious pulses,comprising capacitance means, a charging circuit for said capacitancemeans, means comprising a vacuum tube controlled in accordance with thevoltage across said capacitance means for discharging said capacitancemeans at periodic intervals, and means for decreasing materially thesusceptibility to firing by undesired pulses occurring between saidselected pulses comprising impedance means included in said chargingcircuit, said impedance means being so proportioned with respect to theimpedance constants of said charging circuits that the amplitude ofthevoltage appearing acrosssaid capacitance means at any predeterminedtime during the greater portion of the final half of the charging periodof said capacitance means is substantially less than that resulting froma linear voltagetime characteristic between the same charging voltagelimits of said capacitance means, a vactioned vacuum tube forcontrolling periods of conductivity of said last-mentioned vacuum tube.

8. A, periodic wave generator adapted to be synchronized by selectedpulses of a periodicpulse wave which may include disturbing spuriouspulses, comprising capacitance means, charging ,and discharging circuitsfor said capacitance means, means comprising a vacuum tube having .acontrol electrode for controlling said circuits periodically andalternately to charge and discharge'said capacitance means, saidlast-mentioned means being controlled jointly in accordance with thevoltage of said capacitance means and predetermined pulses of said-waveapplied to said control electrode, and means for decreasing materiallythe susceptibility to synchronization by undesired pulses occurringbetween said seany predetermined time during the greater- 1'50;-

tion of the final half of the active period of said one of said circuitsis substantially less than that resulting from a linear voltage-timecharacteristic between the same chai'ging voltage limits of saidcapacitance means.

. JOHN C. WILSON.

